In a toilet with a low-level water tank, the water tank is generally arranged in a position slightly lower than a seat ring at the rear of the toilet. In the case that the water tank is positioned at the bottom of the water tank and a water level of the water tank is lower than an upper edge of a washing ring, the flushing of the washing ring obviously can not be achieved by conventional gravity drainage. The solution in the conventional technology is that a low-level washing ring flushing device employing the negative pressure principle draws water in the water tank to the washing ring at a higher level by means of a water inlet pressure of tap water, so as to achieve the washing ring flushing.